It is very common to use storage tanks for a variety of fluids such as gasoline, diesel fuel, and oil and these storage tanks are usually filled through openings adjacent to or above the top of the tanks. Such openings usually have relatively small diameters that are sized to receive the dispensing elbow tube of a dispensing tube from a tank truck or other supply source. In most cases, these storage tanks are not equipped with gauges, and the operator filling the storage tank has no direct visual access to the internal space of the storage tank. Additionally, no other additional practical and reliable way of determining whether the storage tank is approaching a full level, while being filled, is generally available.
As a consequence of these factors, proper filling of storage tanks is a universal concern, as overfilling of storage tanks may result in spillage of the tank contents, damage to the tank or filling equipment, contamination of land or ground water, or other serious and potentially dangerous results. Concerns over spillage of the tank contents is particularly acute when the contents being filled into the tank are flammable, toxic and/or environmentally hazardous. The problems associated with overflow spillage from the filling of storage tanks has become so recognized that many local governments now require some liquid storage tanks to be filled only with equipment that automatically shuts off the flow of the liquid to the storage tank when full.
There have been a number of prior attempts to provide an overflow valve to address these problems, however, most of these valves require extensive modification to the existing storage tank set up, such as in Europe where the storage tank is remote or have other less than acceptable attributes. One such valve to be attached to the top of the storage tank is described in U.S. Pat. No. 4,770,317 (Podgers, et al.). In this device, the liquid fill passage is narrowed in diameter at a discrete portion between its inlet and outlet ends to establish a pressure drop in the valve. A pressure responsive latch engages the valve and releasably locks the valve in the open position. A vent passage has one open end in the storage tank at a pre-determined level and another open end communicating with the latch. As liquid flows through the passage, a pressure drop or partial vacuum is formed where the diameter of the passage narrows. The vacuum is vented through the vacuum passage while liquid in the storage tank is below the bottom end of the vent passage. When liquid rises to the level of the end of the vent passage, the pressure causes the latch to release and the valve to close off the passage.
There are, however, several drawbacks to devices such as taught by Podgers, et al. First, the valve must be reopened/reset manually after it is closed. In addition, the housing for this valve is generally not retrofittable to existing storage tank arrangements. Such valves must generally be installed permanently in the ground and secured to the riser pipe extending upwardly from the storage tank. In addition, valves of this type require a relatively high flow rate to effectuate closing of the valve, and the required narrowing of the flow passage limits operable fill rates.
Other valves heretofore available have also been found to be deficient. Some valves require complex installation, where substantial field assembly must be undertaken to custom fit the valve to the storage tank. Other valves have physical structures which cause obstructions in the liquid flow passageway itself, making it difficult or impossible for an operator to insert a dip stick through the valve to manually determine how much liquid is in the storage tank. In many installations, "sticking" is the only way to determine the fluid level of a tank, and the only way to prevent overfilling.
Other prior shut-off valves utilize swing-arm type reciprocating float controls to operate the valve closure in response to the rising fluid level in the tank. Some storage tanks have a permanent riser tube extended upwardly from near the bottom of the storage tank and permanently secured thereto, makes it impossible to use a swing float-type valve as an automatic shut-off valve. Generally, modifications must be made to the riser tube to enable the swing action of the valve within the upper portions of the tank. Examples of such shut-off valves and drop tubes are illustrated in U.S. Pat. No. 4,986,320 to Kesterman, et al. and U.S. Pat. No. 4,667,712 to Draft.
Many previously available valves utilizing float valve activators must also be placed lower in the tank to allow sufficient operating room, thereby also increasing the ullage and effectively limiting the useable volume of the holding tank itself. Many of these valves must also be manually reset once they are triggered closed, in order to prevent further flow of fluid and possible overfilling. This manual reset requirement leaves another possibility for inadvertent failure which can result in overfilling and spills.
Many of the previously available valves do not provide for any misfit between the edge of the valve and the interior wall of the flow passage so that liquid can drain after flow is shut off. Instead, those valves have secondary passageways which allow for slow drainage, sometimes exceeds one minute after the valve is closed.
In the past, many valve assemblies used as a shut-off valve for storage tanks were made to withstand the shock of having flow through the passageway abruptly terminated when the valve closes while liquid is still flowing into the assembly. This configuration requires more material to construct and makes it expensive to manufacture. Also, prior valves require a minimum flow rate through the flow passageway of between 150 and 250 gallons per minute (570 and 950 liters per minute) to be operative. A lower flow rate through the passageway make the valve inoperable and this becomes problematic, especially when filling a storage tank without a pumping mechanism to increase flow of liquid. As a result, it can be seen that the shut-off valves heretofore available have a number of shortcomings, and an improved valve with substantially unencumbered flow characteristics, easily retrofittable onto casting equipment, and featuring improved sensitivity and automatic resetting functions was needed.